That post is very useful as a reference, cheers. I have a much better idea now of the differences.
I have to say though, if the core installation guide says to do "update" and "upgrade", and then the MD says to "update" and "dist-upgrade", surely this has real potential to cause problems? Am I right in saying that if you're going to do a "dist-upgrade" on any of your MDs, you ought to do a "dist-upgrade" on the core first?
FYI, I installed my Zotac Ion without doing "dist-upgrade", OR adding the keys for medibuntu and avenard. What are these keys for exactly? If I add them, is there potential for it to bollox everything up, or is it safe to do regardless of whether they have been folded in or not?